1. Technical Field
The disclosure relates to & method for connecting electrodes of a first circuit member and a second circuit member of which each has an electrode with each other, by using a connection material containing a solder material.
2. Description of the Related Art
In connecting a first circuit, member having a first electrode and a second circuit member having a second electrode with each other, an anisotropic conductive adhesive containing a conductive particle is widely used. The first circuit member and the second circuit member adhere to each other by the anisotropic conductive adhesive, and the first electrode and the second electrode are electrically connected to each other by the conductive particle.
As the conductive particle of the anisotropic conductive adhesive, for example, a gold-plated nickel particle or a metal-plated resin particle is used. The nickel particle or the resin particle achieves electric connection with the electrode by coining into contact with the electrode in a state of being compressed between the electrodes. In order to achieve the electric connection by bringing the electrode and the conductive particle into contact with each other, a high pressure (for example, 50 MPa to 150 MPa) is necessary.
In addition, the connection between the circuit members by the anisotropic conductive adhesive is performed by thermocompression bonding, for example, under the temperature of approximately 200° C. Therefore, when a high pressure is applied to the anisotropic conductive adhesive interposed between the first circuit member and the second circuit member, viscosity of the adhesive largely deteriorates, and fluidity increases. Therefore, the conductive particle is likely to be pushed out to the periphery thereof from a part between the electrodes together with the adhesive, and is unlikely to efficiently capture the conductive particle between the electrodes. In addition, since the pressure applied to each of the circuit members is high and the thermal stress applied to the circuit member is also high, in a case where the circuit member is thin and the strength thereof is low, a defect, such as a curve of the circuit member, is likely to be generated.
Here, achievement of the electric connection by wetting between the electrode and a molten solder by using a solder particle instead, of the conductive particle, is investigated. For example, Japanese Patent Unexamined Publication No. H08-186156 suggests to heat a thermosetting adhesive containing the solder particle in two steps during the thermocompression bonding. Specifically, the thermosetting adhesive is temporarily heated to a temperature at which the solder particle is not melted, the adhesive is hardened to a certain extent, and then, the adhesive is mainly heated at a temperature at which the solder particle is melted, and the adhesive is completely hardened. Accordingly, an excessive flow of the molten solder is suppressed.
In FIG. 3, an example of a temperature profile of the adhesive in a thermocompression bonding process and a pressure profile applied to the solder particle is illustrated. In FIG. 3, a solid line illustrates the pressure profile, and a one-dot chain line illustrates the temperature profile. In an initial stage (from time t11 to t12) of the thermocompression bonding, the adhesive containing the solder particle is heated at a temperature T11 lower than a melting point Tm of the solder material, and a pressure of P11 is applied to the solder particle. After this, a heating temperature is increased, and after a time t13, main heating is performed at a temperature T12 that exceeds the melting point Tm. In the main heating, when the solder particle is melted and wet-spreads to the electrode and the heating is finished, the solder is solidified and the electric connection is achieved.